1. Field of the Invention
This invention relates to the reaction of asphalt and polymers to produce an improved polymer-linked-asphalt product. More particularly, the present invention relates to the reaction and resultant linking of a combination of epoxide-containing polymers and anhydride-containing polymers to asphalt forming a polymer-linked-asphalt composition having unique properties. The improved polymer-linked-asphalt product is particularly useful in roofing applications.
2. Description of the Related Art
The use of polymers as additives to asphalt (bitumen) is well known in the art. See for example U.S. Pat. Nos. 4,650,820 and 4,451,598, both incorporated herein by reference, wherein terpolymers derived from ethylene, an alkyl acrylate and maleic anhydride are mixed with bitumen. Also, see for example U.S. Pat. Nos. 5,306,750 and 6,117,926, both incorporated by reference, wherein reactant epoxy-functionalized, particularly glycidyl-containing, ethylene terpolymers are mixed and reacted with bitumen and, preferably (as taught in U.S. Pat. No. 6,117,926) with a catalyst to accelerate the rate of reaction and reduce the cost of the modified system.
Also disclosed in a trade brochure by ORKEM is the use of terpolymers prepared from ethylene, an alkyl acrylate and either maleic anhydride or glycidyl methacrylate as enhancement additives for bitumen and tar.
U.S. Pat. No. 4,301,051 discloses a chemically modified asphalt prepared by first reacting an asphalt with (1) a polymerizable vinyl aromatic monomer and (2) a rubbery polymer, and then reacting the product with a cross linking agent. The cross linking agents disclosed include organic polyisocyanates, polyepoxide monomers having molecular weights in the range from of 140 (RD4) to 420 (Araldite 508) and organic polycarboxylic acids or anhydrides.
Polymer-linked-asphalt compositions wherein the polymer modifiers include a reactant ethylene/alkyl acrylate/glycidyl methacrylate terpolymer and a high density polyethylene (HDPE)/maleic anhydride graft copolymer are described in PCT Patent Application Publication WO03/002671.
While it is possible to produce useful polymer-modified asphalt using the processes described in these references there is still a need for polymer-modified asphalt with improved high temperature resistance as well as improved elasticity at both ambient and low temperatures. There is also a need to provide polymer-modified asphalt that has good toughness and tenacity.
Asphalt is used in a variety of waterproofing and roofing applications. An important property of an asphalt roofing material is its softening point at elevated temperatures. Higher temperature softening points provide a more mechanically durable surface (for example, resistance to penetration or deformation caused by weight on the roofing surface) particularly when the material is at an elevated temperature.
Also, new performance criteria are continually sought by various construction and roofing practitioners, necessitating the development of improved asphalt products.